Figure 3.

Frequency-specificity of brain oscillations. (A) Time-frequency power of the signals by means of a complex Morlet’s wavelet transform applied on the average SEP for each participant, then averaged across participants. Evoked gamma activity is strictly phase-locked to the electrical stimulus. The mean Cz SEP curves were superimposed on time frequency analyses for comparison. Dashed line indicates the moment of the stimulation in the “Loaded minus Control” panel. (B) Source localization of beta (20 Hz) frequency band oscillations (right panel). In contrast to primary somatosensory cortex (SI; left panel, top view), secondary somatosensory cortex (SII) showed bilateral activation even with unilateral peripheral activation likely due both to parallel thalamic projections and to serial activation via cortico-cortical and transcallosal fibers (Eickhoff et al., 2007). In the bottom view, the temporal lobes were removed by tranparency artifact for display purposes. The evoked stimulation in the SI showing a lateralized activation at the N90 latency response was included to assess the effectiveness and specificity of applied unilateral left foot stimulation (left panel).